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<H1>Iperf version 2.0.5</H1>

<H3>May 2004</H3>

<HR><!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- -->

<H3>NLANR applications support
<BR><A HREF="http://dast.nlanr.net/">http://dast.nlanr.net/</A>
<BR><A HREF="mailto:dast@nlanr.net">&lt;dast@nlanr.net&gt;</A>
</H3>
<P><FONT face="arial,helvetica">
<H1>Iperf User Docs</H1>
<H4>Mark Gates<br>
    Ajay Tirumala<BR>
    Jon Dugan<BR>
    Kevin Gibbs<BR> </H4>

May 2004 
<P></CENTER>
[<a href="#compiling">Compiling</A> | 
<A href="#features">Features</A>&nbsp; | 
<A href="#tuningtcp">Tuning a TCP connection</A> | 
<A href="#tuningudp">Tuning a UDP connection</A> | 
<A href="#multicast">Running multicast servers and clients</A> | 
<A href="#ipv6">IPv6 Mode</A> | 
<A href="#repmode">Representative Streams</A> |
<A href="#daemon"> Running Iperf as a daemon</A> |
<!--<A href="#adaptive">Adaptive Window Sizes</A> | --> 
<A href="#service">Running Iperf as a Windows Service</A> ] 
<HR>
<!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- -->
<H2><A name=compiling></A>Compiling</H2>

Once you have the distribution, on UNIX, 
unpack it using gzip and tar. That will create a new directory 
'iperf-&lt;version#&gt;' with the source files and documentation. 
<P>

Iperf compiles cleanly on many systems including Linux, SGI IRIX, HP-UX, 
Solaris, AIX, and Cray UNICOS. Use '<TT>make</TT>' to configure for your OS and 
compile the source code. 

<BLOCKQUOTE><PRE>

gunzip -c iperf-&lt;version&gt;.tar.gz | tar -xvf -
cd iperf-&lt;version&gt;
./configure
make

</PRE></BLOCKQUOTE>

To install iperf, use '<TT>make install</TT>', 
which will ask you where to install it. To recompile, the easiest way is to 
start over. Do '<TT>make distclean</TT>' then '<TT>./configure; make</TT>'. See the Makefile 
for more options. 
<P>

If you have problems, please report them to <A href="mailto:dast@nlanr.net">dast@nlanr.net</A> and 
we will try to fix them quickly. <BR>

<HR>
<!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- -->

<H2><A name=features></A>Features</H2>
<UL>
  <LI>TCP 
  <UL>
    <LI>Measure bandwidth 
    <LI>Report MSS/MTU size and observed read sizes. 
    <LI>Support for TCP window size via socket buffers. 
    <LI>Multi-threaded if pthreads or Win32 threads are available. Client and 
    server can have multiple simultaneous connections. 
 <!--   <LI>Suggest the optimal window size for a connection where the OS allows 
    setting window sizes in the granularity of bytes. </LI>--></UL>
  <LI>UDP 
  <UL>
    <LI>Client can create UDP streams of specified bandwidth. 
    <LI>Measure packet loss 
    <LI>Measure delay jitter 
    <LI>Multicast capable 
    <LI>Multi-threaded if pthreads are available. Client and server can have 
    multiple simultaneous connections. (This doesn't work in Windows.) </LI></UL>
  <LI>Where appropriate, options can be specified with K (kilo-) and M (mega-) 
  suffices. So 128K instead of 131072 bytes. 
  <LI>Can run for specified time, rather than a set amount of data to transfer. 
  <LI>Picks the best units for the size of data being reported. 
  <LI>Server handles multiple connections, rather than quitting after a single 
  test. 
  <LI>Print periodic, intermediate bandwidth, jitter, and loss reports at 
  specified intervals. 
  <LI>Run the server as a daemon (Check out <A 
  href="http://www-itg.lbl.gov/nettest">Nettest</A> for running it as a secure 
  daemon). 
  <LI>Run the server as a Windows NT Service 
  <LI>Use representative streams to test out how link layer compression affects 
  your achievable bandwidth. 

<!--  <LI>A library of <A 
  href="lib.html">useful functions and C++ 
  classes.</A> </LI>
-->
</UL>
<HR>
<!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --><BR>&nbsp; 

<TABLE cellPadding=3 border=1>
  <TBODY>
  <TR vAlign=top>
    <TH align=left>Command line option</TH>
    <TH align=left>Environment variable option</TH>
    <TH align=left>Description</TH></TR>
  <TR>
    <TH bgColor=#cccccc colSpan=3>Client and Server options</TH></TR>
  <TR vAlign=top>
    <TD><A name=format></A><TT>-f, --format <I>[bkmgaBKMGA]</I></TT></TD>
    <TD><TT>$IPERF_FORMAT</TT></TD>
    <TD>A letter specifying the format to print bandwidth numbers in. 
      Supported formats are&nbsp; 
	<PRE>
&nbsp;&nbsp;&nbsp; 'b' = bits/sec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'B' = Bytes/sec
&nbsp;&nbsp;&nbsp; 'k' = Kbits/sec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'K' = KBytes/sec
&nbsp;&nbsp;&nbsp; 'm' = Mbits/sec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'M' = MBytes/sec
&nbsp;&nbsp;&nbsp; 'g' = Gbits/sec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 'G' = GBytes/sec
&nbsp;&nbsp;&nbsp; 'a' = adaptive bits/sec&nbsp;&nbsp; 'A' = adaptive Bytes/sec
	</PRE>
	The adaptive formats choose between kilo- and mega- as appropriate. Fields 
      other than bandwidth always print bytes, but otherwise follow the 
      requested format. Default is 'a'.&nbsp; <BR><I>NOTE:</I> here Kilo = 1024, 
      Mega = 1024^2 and Giga = 1024^3 when dealing with bytes. Commonly in networking, 
      Kilo = 1000, Mega = 1000^2, and Giga = 1000^3 so we  use this when dealing with
      bits. If this really bothers you, use -f b and do the math.</TD></TR>
  <TR vAlign=top>
    <TD><A name=interval></A><TT>-i, --interval <I>#</I></TT></TD>
    <TD><TT>$IPERF_INTERVAL</TT></TD>
    <TD>Sets the interval time in seconds between periodic bandwidth, jitter, 
      and loss reports. If non-zero, a report is made every <I>interval</I> 
      seconds of the bandwidth since the last report. If zero, no periodic 
      reports are printed. Default is zero.</TD></TR>
  <TR vAlign=top>
    <TD><A name=len></A><TT>-l, --len <I>#[KMG]</I></TT></TD>
    <TD><TT>$IPERF_LEN</TT></TD>
    <TD>The length of buffers to read or write. Iperf works by writing an 
      array of <I>len</I> bytes a number of times. Note for UDP, this is the 
      datagram size and needs to be lowered when using IPv6 addressing to 1450 
      or less to avoid fragmentation. See also the <A href="#num">-n</A> and <A 
      href="#time">-t</A> 
      options.</TD></TR>
  <TR vAlign=top>
    <TD><A name=print_mss></A><TT>-m, --print_mss</TT></TD>
    <TD><TT>$IPERF_PRINT_MSS</TT></TD>
    <TD>Print the reported TCP MSS size (via the TCP_MAXSEG option) and the 
      observed read sizes which often correlate with the MSS. The MSS is usually 
      the MTU - 40 bytes for the TCP/IP header. Often a slightly smaller MSS is 
      reported because of extra header space from IP options. The interface type 
      corresponding to the MTU is also printed (ethernet, FDDI, etc.). This 
      option is not implemented on many OSes, but the read sizes may still 
      indicate the MSS.</TD></TR>
  <TR vAlign=top>
    <TD><A name=port></A><TT>-p, --port <I>#</I></TT></TD>
    <TD><TT>$IPERF_PORT</TT></TD>
    <TD>The server port for the server to listen on and the client to connect 
      to. This should be the same in both client and server. Default is 5001, 
      the same as ttcp.</TD></TR>
  <TR vAlign=top>
    <TD><A name=udp></A><TT>-u, --udp</TT></TD>
    <TD><TT>$IPERF_UDP</TT></TD>
    <TD>Use UDP rather than TCP. See also the <A 
      href="#bandwidth">-b</A> 
      option.</TD></TR>
  <TR vAlign=top>
    <TD><A name=window></A><TT>-w, --window <I>#[KMG]</I></TT></TD>
    <TD><TT>$TCP_WINDOW_SIZE</TT></TD>
    <TD>Sets the socket buffer sizes to the specified value. For TCP, this 
      sets the TCP window size. For UDP it is just the buffer which datagrams 
      are received in, and so limits the largest receivable datagram size.</TD></TR>
  <TR vAlign=top>
    <TD><A name=bind></A><TT>-B, --bind <I>host</I></TT></TD>
    <TD><TT>$IPERF_BIND</TT></TD>
    <TD>Bind to <I>host</I>, one of this machine's addresses. For the client 
      this sets the outbound interface. For a server this sets the incoming 
      interface. This is only useful on multihomed hosts, which have multiple 
      network interfaces.&nbsp; 
      <P>For Iperf in UDP server mode, this is also used to bind and join to a 
      multicast group. Use addresses in the range 224.0.0.0 to 239.255.255.255 
      for multicast. See also the <A 
      href="#ttl">-T</A> 
      option.</P></TD></TR>
  <TR vAlign=top>
    <TD><A name=compatibility></A><TT>-C, --compatibility </TT></TD>
    <TD><TT>$IPERF_COMPAT</TT></TD>
    <TD>Compatibility mode allows for use with older version of iperf. This mode
        is not required for interoperability but it is highly recommended. In
        some cases when using representative streaming you could cause a 1.7 server
        to crash or cause undesired connection attempts.</P></TD></TR>
  <TR vAlign=top>
    <TD><A name=mss></A><TT>-M, --mss <I>#[KMG]</I></TT></TD>
    <TD><TT>$IPERF_MSS</TT></TD>
    <TD>Attempt to set the TCP maximum segment size (MSS) via the TCP_MAXSEG 
      option. The MSS is usually the MTU - 40 bytes for the TCP/IP header. For 
      ethernet, the MSS is 1460 bytes (1500 byte MTU). This option is not 
      implemented on many OSes.</TD></TR>
  <TR vAlign=top>
    <TD><A name=nodelay></A><TT>-N, --nodelay</TT></TD>
    <TD><TT>$IPERF_NODELAY</TT></TD>
    <TD>Set the TCP no delay option, disabling Nagle's algorithm. Normally 
      this is only disabled for interactive applications like telnet.</TD></TR>
  <TR>
    <TD><TT>-V </TT>(from v1.6 or higher)</TD>
    <TD>.</TD>
    <TD>Bind to an IPv6 address <BR>Server side: <BR>$ iperf -s -V&nbsp; 
      <P>Client side: <BR>$ iperf -c &lt;Server IPv6 Address&gt; -V 
      <BR>&nbsp;</P>Note: On version 1.6.3 and later a specific IPv6 Address does
      not need to be bound with the <A href="#bind">-B</A> option, previous 1.6 
      versions do. Also on most OSes using this option will also respond to IPv4
      clients using IPv4 mapped addresses.</TD></TR>
  <TR>
    <TH bgColor=#cccccc colSpan=3>Server specific options</TH></TR>
  <TR vAlign=top>
    <TD><A name=server></A><TT>-s, --server</TT></TD>
    <TD><TT>$IPERF_SERVER</TT></TD>
    <TD>Run Iperf in server mode.</TD></TR>
  <TR>
    <TD><TT>-D </TT> (from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Run the server as a daemon (Unix platforms) <BR>On Win32 platforms 
      where services are available, Iperf will start running as a service.</TD></TR>
  <TR>
    <TD><TT>-R </TT>(only for Windows, from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Remove the Iperf service (if it's running).&nbsp;</TD></TR><TR>
    <TD><TT>-o </TT>(only for Windows, from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Redirect output to given file.&nbsp;</TD></TR>
  <TR vAlign=top>
    <TD><A name=sclient></A><TT>-c, --client <I>host</I></TT></TD>
    <TD><TT>$IPERF_CLIENT</TT></TD>
    <TD> If Iperf is in server mode, then specifying a host with -c
        will limit the connections that Iperf will accept to the
        <I>host</I> specified. Does not work well for UDP.</TD></TR>
  <TR vAlign=top>
    <TD><A name=sparallel></A><TT>-P, --parallel <I>#</I></TT></TD>
    <TD><TT>$IPERF_PARALLEL</TT></TD>
    <TD>The number of connections to handle by the server before
      closing. Default is 0 (which means to accept connections forever).</TD></TR>
  <TR vAlign=top>
    <TD><A name=ssingle></A><TT>-1, --singleclient</TT></TD>
    <TD>.</TD>
    <TD>Instruct the iperf server to accept only a single client connection 
        before terminating.</TD></TR>
  <TR>
    <TH bgColor=#cccccc colSpan=3>Client specific options</TH></TR>
  <TR vAlign=top>
    <TD><A name=bandwidth></A><TT>-b, --bandwidth <I>#[KMG]</I></TT></TD>
    <TD><TT>$IPERF_BANDWIDTH</TT></TD>
    <TD>The UDP bandwidth to send at, in bits/sec. This implies the -u option. 
      Default is 1 Mbit/sec.</TD></TR>
  <TR vAlign=top>
    <TD><A name=client></A><TT>-c, --client <I>host</I></TT></TD>
    <TD><TT>$IPERF_CLIENT</TT></TD>
    <TD>Run Iperf in client mode, connecting to an Iperf server running on 
      <I>host</I>.</TD></TR>
  <TR vAlign=top>
    <TD><A name=dualtest></A><TT>-d, --dualtest </TT></TD>
    <TD><TT>$IPERF_DUALTEST</TT></TD>
    <TD>Run Iperf in dual testing mode. This will cause the server to connect
        back to the client on the port specified in the
        <A href="#listenport">-L</A> option (or defaults
        to the port the client connected to the server on). This is done immediately
        therefore running the tests simultaneously. If you want an alternating
        test try <A href="#tradeoff">-r.</A></TD></TR>
  <TR vAlign=top>
    <TD><A name=num></A><TT>-n, --num <I>#[KM]</I></TT></TD>
    <TD><TT>$IPERF_NUM</TT></TD>
    <TD>The number of buffers to transmit. Normally, Iperf sends for 10 
      seconds. The -n option overrides this and sends an array of <I>len</I> 
      bytes <I>num</I> times, no matter how long that takes. See also the <A 
      href="#len">-l</A> 
      and <A 
      href="#time">-t</A> 
      options.</TD></TR>
  <TR vAlign=top>
    <TD><A name=tradeoff></A><TT>-r, --tradeoff </TT></TD>
    <TD><TT>$IPERF_TRADEOFF</TT></TD>
    <TD>Run Iperf in tradeoff testing mode. This will cause the server to connect
        back to the client on the port specified in the
        <A href="#listenport">-L</A> option (or defaults
        to the port the client connected to the server on). This is done following
        the client connection termination, therefore running the tests
        alternating. If you want an simultaneous test try
        <A href="#dualtest">-d.</A></TD></TR>
  <TR vAlign=top>
    <TD><A name=time></A><TT>-t, --time <I>#</I></TT></TD>
    <TD><TT>$IPERF_TIME</TT></TD>
    <TD>The time in seconds to transmit for. Iperf normally works by 
      repeatedly sending an array of <I>len</I> bytes for <I>time</I> seconds. 
      Default is 10 seconds. See also the <A 
      href="#len">-l</A> 
      and <A 
      href="#num">-n</A> 
      options.</TD></TR>
  <TR vAlign=top>
    <TD><A name=listenport></A><TT>-L, --listenport <I>#</I></TT></TD>
    <TD><TT>$IPERF_LISTENPORT</TT></TD>
    <TD>This specifies the port that the server will connect back to the
        client on. It defaults to the port used to connect to the server
        from the client.</TD></TR>
  <TR vAlign=top>
    <TD><A name=parallel></A><TT>-P, --parallel <I>#</I></TT></TD>
    <TD><TT>$IPERF_PARALLEL</TT></TD>
    <TD>The number of simultaneous connections to make to the server. Default 
      is 1. Requires thread support on both the client and server.</TD></TR>
  <TR vAlign=top>
    <TD><A name=tos></A><TT>-S, --tos <I>#</I></TT></TD>
    <TD><TT>$IPERF_TOS</TT></TD>
    <TD>The type-of-service for outgoing packets. (Many routers ignore the TOS 
      field.) You may specify the value in hex with a '0x' prefix, in octal with 
      a '0' prefix, or in decimal. For example, '0x10' hex = '020' octal = '16' 
      decimal. The TOS numbers specified in RFC 1349 are:&nbsp; 
	<PRE>
&nbsp;&nbsp;&nbsp; IPTOS_LOWDELAY&nbsp;&nbsp;&nbsp;&nbsp; minimize delay&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0x10
&nbsp;&nbsp;&nbsp; IPTOS_THROUGHPUT&nbsp;&nbsp; maximize throughput&nbsp;&nbsp; 0x08
&nbsp;&nbsp;&nbsp; IPTOS_RELIABILITY&nbsp; maximize reliability&nbsp; 0x04
&nbsp;&nbsp;&nbsp; IPTOS_LOWCOST&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; minimize cost&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0x02
&nbsp;&nbsp;&nbsp;&nbsp;
	</PRE>
	</TD></TR>
  <TR vAlign=top>
    <TD><A name=ttl></A><TT>-T, --ttl <I>#</I></TT></TD>
    <TD><TT>$IPERF_TTL</TT></TD>
    <TD>The time-to-live for outgoing multicast packets. This is essentially 
      the number of router hops to go through, and is also used for scoping. 
      Default is 1, link-local.</TD></TR>
  <TR>
    <TD><TT>-F</TT> (from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Use a representative stream to measure bandwidth, e.g. :-&nbsp; <BR>$ 
      iperf -c &lt;server address&gt; -F &lt;file-name&gt;</TD></TR>
  <TR>
    <TD><TT>-I </TT>(from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Same as -F, input from stdin.</TD></TR>
 <!-- <TR>
    <TD><TT>-W </TT>(from v1.2 or higher)</TD>
    <TD>.</TD>
    <TD>Adaptive Window Sizes.
	  <BR>Use Iperf to suggest the best Window size for a connection. Iperf will start from a default window size and try to perform a search for the optimal window size</TD></TR>
-->  <TR>
    <TH bgColor=#cccccc colSpan=3>Miscellaneous options</TH></TR>
  <TR vAlign=top>
    <TD><A name=help></A><TT>-h, --help</TT></TD>
    <TD>&nbsp;</TD>
    <TD>Print out a summary of commands and quit.</TD></TR>
  <TR vAlign=top>
    <TD><A name=version></A><TT>-v, --version</TT></TD>
    <TD>&nbsp;</TD>
    <TD>Print version information and quit. Prints 'pthreads' if compiled with 
      POSIX threads, 'win32 threads' if compiled with Microsoft Win32 threads, 
      or 'single threaded' if compiled without threads.</TD></TR></TBODY></TABLE>
<P>
<HR>
<!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- -->
<H2><A name=tuningtcp></A>Tuning a TCP connection</H2>

The primary goal of Iperf 
is to help in tuning TCP connections over a particular path. The most 
fundamental tuning issue for TCP is the TCP window size, which controls how much 
data can be in the network at any one point. If it is too small, the sender will 
be idle at times and get poor performance. The theoretical value to use for the 
TCP window size is the <I>bandwidth delay product</I>, 
<BLOCKQUOTE>bottleneck bandwidth * round trip time</BLOCKQUOTE>In the below 
modi4/cyclops example, the bottleneck link is a 45 Mbit/sec DS3 link and the 
round trip time measured with ping is 42 ms. The bandwidth delay product is 
<BLOCKQUOTE>45 Mbit/sec * 42 ms <BR>= (45e6) * (42e-3) <BR>= 1890000 bits 
  <BR>= 230 KByte</BLOCKQUOTE>That is a starting point for figuring the best 
window size; setting it higher or lower may produce better results. In our 
example, buffer sizes over 130K did not improve the performance, despite the 
bandwidth delay product of 230K. 
<P>Note that many OSes and hosts have upper limits on the TCP window size. These 
may be as low as 64 KB, or as high as several MB. Iperf tries to detect when 
these occur and give a warning that the actual and requested window sizes are 
not equal (as below, though that is due to rounding in IRIX). PSC has a <A 
href="http://www.psc.edu/networking/perf_tune.html">list detailing</A> how to 
change the default and maximum window sizes for various OSes. For more 
information on TCP window sizes, see the <A 
href="http://dast.nlanr.net/Guides/GettingStarted/TCP_window_size.html">User's 
Guide to TCP Windows.</A> 
<P>Here is an example session, between node1 in Illinois and node2 in North 
Carolina. These are connected via the vBNS backbone and a 45 Mbit/sec DS3 link. 
Notice we improve bandwidth performance by a factor of 3 using proper TCP window 
sizes. Use the adaptive window sizes feature on platforms which allow setting 
window sizes in the granularity of bytes. 
<BLOCKQUOTE>
<PRE>
<B>node2&gt;</B> iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 60.0 KByte (default)
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node1&gt; port 2357
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0-10.1 sec&nbsp;&nbsp; 6.5 MBytes&nbsp;&nbsp; <B><FONT color=#ff0000>5.2 Mbits/sec

</FONT>node1&gt;</B> iperf -c node2
------------------------------------------------------------
Client connecting to node1, TCP port 5001
TCP window size: 59.9 KByte (default)
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node1&gt; port 2357 connected with &lt;IP Addr node2&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0-10.0 sec&nbsp;&nbsp; 6.5 MBytes&nbsp;&nbsp; 5.2 Mbits/sec</PRE>
  <HR>
<PRE><B>node2&gt;</B> iperf -s -w 130k
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:&nbsp; 130 KByte
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node 2&gt; port 5001 connected with &lt;IP Addr node 1&gt; port 2530
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0-10.1 sec&nbsp; 19.7 MBytes&nbsp; <B><FONT color=#ff0000>15.7 Mbits/sec

</FONT>node1&gt;</B> iperf -c node2 -w 130k
------------------------------------------------------------
Client connecting to node2, TCP port 5001
TCP window size:&nbsp; 129 KByte (WARNING: requested&nbsp; 130 KByte)
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node1&gt; port 2530 connected with &lt;IP Addr node2&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0-10.0 sec&nbsp; 19.7 MBytes&nbsp; 15.8 Mbits/sec</PRE></BLOCKQUOTE>Another 
test to do is run parallel TCP streams. If the total aggregate bandwidth is more 
than what an individual stream gets, something is wrong. Either the TCP window 
size is too small, or the OS's TCP implementation has bugs, or the network 
itself has deficiencies. See above for TCP window sizes; otherwise diagnosing 
which is somewhat difficult. If Iperf is compiled with pthreads, a single client 
and server can test this, otherwise setup multiple clients and servers on 
different ports. Here's an example where a single stream gets 16.5 Mbit/sec, but 
two parallel streams together get 16.7 + 9.4 = 26.1 Mbit/sec, even when using 
large TCP window sizes: 
<BLOCKQUOTE><PRE><B>node2&gt;</B> iperf -s -w 300k
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:&nbsp; 300 KByte
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node1&gt; port 6902
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0-10.2 sec&nbsp; 20.9 MBytes&nbsp; <B><FONT color=#ff0000>16.5 Mbits/sec

</FONT></B>[&nbsp; 4] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node1&gt; port 6911
[&nbsp; 5] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node2&gt; port 6912
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 5]&nbsp; 0.0-10.1 sec&nbsp; 21.0 MBytes&nbsp; <B><FONT color=#ff0000>16.7 Mbits/sec
</FONT></B>[&nbsp; 4]&nbsp; 0.0-10.3 sec&nbsp; 12.0 MBytes&nbsp;&nbsp;<B><FONT color=#ff0000> 9.4 Mbits/sec

</FONT>node1&gt;</B> ./iperf -c node2 -w 300k
------------------------------------------------------------
Client connecting to node2, TCP port 5001
TCP window size:&nbsp; 299 KByte (WARNING: requested&nbsp; 300 KByte)
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node2&gt; port 6902 connected with &lt;IP Addr node1&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0-10.2 sec&nbsp; 20.9 MBytes&nbsp; 16.4 Mbits/sec

<B>node1&gt;</B> iperf -c node2 -w 300k -P 2
------------------------------------------------------------
Client connecting to node2, TCP port 5001
TCP window size:&nbsp; 299 KByte (WARNING: requested&nbsp; 300 KByte)
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node2&gt; port 6912 connected with &lt;IP Addr node1&gt; port 5001
[&nbsp; 3] local &lt;IP Addr node2&gt; port 6911 connected with &lt;IP Addr node1&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0-10.1 sec&nbsp; 21.0 MBytes&nbsp; 16.6 Mbits/sec
[&nbsp; 3]&nbsp; 0.0-10.2 sec&nbsp; 12.0 MBytes&nbsp;&nbsp; 9.4 Mbits/sec</PRE></BLOCKQUOTE>A 
secondary tuning issue for TCP is the maximum transmission unit (MTU). To be 
most effective, both hosts should support Path MTU Discovery. PSC has a <A 
href="http://www.psc.edu/networking/perf_tune.html">list detailing</A> what OSes 
support Path MTU Discovery. Hosts without Path MTU Discovery often use 536 as 
the MSS, which wastes bandwidth and processing time. Use the -m option to 
display what MSS is being used, and see if this matches what you expect. Often 
it is around 1460 bytes for ethernet. 
<BLOCKQUOTE><PRE><B>node3&gt;</B> iperf -s -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 60.0 KByte (default)
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node3&gt; port 5001 connected with &lt;IP Addr node4&gt; port 1096
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0- 2.0 sec&nbsp;&nbsp; 1.8 MBytes&nbsp;&nbsp; 6.9 Mbits/sec
[&nbsp; 4] <B><FONT color=#ff0000>MSS size 1448 bytes (MTU 1500 bytes, ethernet)
</FONT></B>[&nbsp; 4] Read lengths occurring in more than 5% of reads:
[&nbsp; 4]&nbsp;&nbsp; 952 bytes read&nbsp;&nbsp; 219 times (16.2%)
[&nbsp; 4]&nbsp; 1448 bytes read&nbsp; 1128 times (83.6%)</PRE></BLOCKQUOTE>Here 
is a host that doesn't support Path MTU Discovery. It will only send and receive 
small 576 byte packets. 
<BLOCKQUOTE><PRE><B>node4&gt;</B> iperf -s -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 32.0 KByte (default)
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node4&gt; port 5001 connected with &lt;IP Addr node3&gt; port 13914
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 4]&nbsp; 0.0- 2.3 sec&nbsp;&nbsp; 632 KBytes&nbsp;&nbsp; 2.1 Mbits/sec
<B><FONT color=#ff0000>WARNING: Path MTU Discovery may not be enabled.
</FONT></B>[&nbsp; 4] <B><FONT color=#ff0000>MSS size 536 bytes (MTU 576 bytes, minimum)
</FONT></B>[&nbsp; 4] Read lengths occurring in more than 5% of reads:
[&nbsp; 4]&nbsp;&nbsp; 536 bytes read&nbsp;&nbsp; 308 times (58.4%)
[&nbsp; 4]&nbsp; 1072 bytes read&nbsp;&nbsp;&nbsp; 91 times (17.3%)
[&nbsp; 4]&nbsp; 1608 bytes read&nbsp;&nbsp;&nbsp; 29 times (5.5%)</PRE></BLOCKQUOTE>Iperf 
supports other tuning options, which were added for exceptional network 
situations like HIPPI-to-HIPPI over ATM. <BR>
<HR>
<!-- ----- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- -->

<H2><A name=tuningudp></A>Tuning a UDP connection</H2>

Iperf creates a constant bit rate UDP stream. This is a very artificial 
stream, similar to voice communication but not much else. 
<P>

You will want to adjust the datagram size (-l) to the size your application 
uses. 
<P>

The server detects UDP datagram loss by ID numbers in the datagrams. Usually 
a UDP datagram becomes several IP packets. Losing a single IP packet will lose 
the entire datagram. To measure packet loss instead of datagram loss, make the 
datagrams small enough to fit into a single packet, using the -l option. The 
default size of 1470 bytes works for ethernet. Out-of-order packets are also 
detected. (Out-of-order packets cause some ambiguity in the lost packet count; 
Iperf assumes they are not duplicate packets, so they are excluded from the lost 
packet count.) Since TCP does not report loss to the user, I find UDP tests 
helpful to see packet loss along a path. 
<P>

Jitter calculations are continuously computed by the server, as specified by 
RTP in RFC 1889. The client records a 64 bit second/microsecond timestamp in the 
packet. The server computes the relative transit time as (server's receive time 
- client's send time). The client's and server's clocks do not need to be 
synchronized; any difference is subtracted out in the jitter calculation. Jitter 
is the smoothed mean of differences between consecutive transit times. 
<BLOCKQUOTE><PRE><B>node2&gt;</B> iperf -s -u -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Receiving 1470 byte datagrams
UDP buffer size: 60.0 KByte (default)
------------------------------------------------------------
[&nbsp; 4] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node1&gt; port 9726
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Jitter&nbsp;&nbsp; Lost/Total Datagrams
[&nbsp; 4]&nbsp; 0.0- 1.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.209 ms&nbsp;&nbsp;&nbsp; 1/&nbsp; 894 (0.11%)
[&nbsp; 4]&nbsp; 1.0- 2.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.221 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 2.0- 3.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.277 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 3.0- 4.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.359 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 893 (0%)
[&nbsp; 4]&nbsp; 4.0- 5.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.251 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 5.0- 6.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.215 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 6.0- 7.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.325 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 7.0- 8.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.254 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 8.0- 9.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.282 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 892 (0%)
[&nbsp; 4]&nbsp; 0.0-10.0 sec&nbsp; 12.5 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.243 ms&nbsp;&nbsp;&nbsp; 1/ 8922 (0.011%)

<B>node1&gt;</B> iperf -c node2 -u -b 10m
------------------------------------------------------------
Client connecting to node2, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size: 60.0 KByte (default)
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node1&gt; port 9726 connected with &lt;IP Addr node2&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0-10.0 sec&nbsp; 12.5 MBytes&nbsp; 10.0 Mbits/sec
[&nbsp; 3] Sent 8922 datagrams</PRE></BLOCKQUOTE>Notice the higher jitter due to 
datagram reassembly when using larger 32 KB datagrams, each split into 23 
packets of 1500 bytes. The higher datagram loss seen here may be due to the 
burstiness of the traffic, which is 23 back-to-back packets and then a long 
pause, rather than evenly spaced individual packets. 
<BLOCKQUOTE><PRE><B>node2&gt;</B> iperf -s -u -l 32k -w 128k -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Receiving 32768 byte datagrams
UDP buffer size:&nbsp; 128 KByte
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node2&gt; port 5001 connected with &lt;IP Addr node1&gt; port 11303
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Jitter&nbsp;&nbsp; Lost/Total Datagrams
[&nbsp; 3]&nbsp; 0.0- 1.0 sec&nbsp;&nbsp; 1.3 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.430 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 41 (0%)
[&nbsp; 3]&nbsp; 1.0- 2.0 sec&nbsp;&nbsp; 1.1 MBytes&nbsp;&nbsp; 8.5 Mbits/sec&nbsp; 5.996 ms&nbsp;&nbsp;&nbsp; 6/&nbsp;&nbsp; 40 (15%)
[&nbsp; 3]&nbsp; 2.0- 3.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp;&nbsp; 9.7 Mbits/sec&nbsp; 0.796 ms&nbsp;&nbsp;&nbsp; 1/&nbsp;&nbsp; 40 (2.5%)
[&nbsp; 3]&nbsp; 3.0- 4.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.403 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 4.0- 5.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.448 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 5.0- 6.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.464 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 6.0- 7.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.442 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 7.0- 8.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.342 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 8.0- 9.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.431 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 9.0-10.0 sec&nbsp;&nbsp; 1.2 MBytes&nbsp; 10.0 Mbits/sec&nbsp; 0.407 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 40 (0%)
[&nbsp; 3]&nbsp; 0.0-10.0 sec&nbsp; 12.3 MBytes&nbsp;&nbsp; 9.8 Mbits/sec&nbsp; 0.407 ms&nbsp;&nbsp;&nbsp; 7/&nbsp; 401 (1.7%)

<B>node1&gt;</B> iperf -c node2 -b 10m -l 32k -w 128k
------------------------------------------------------------
Client connecting to node2, UDP port 5001
Sending 32768 byte datagrams
UDP buffer size:&nbsp; 128 KByte
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node2&gt; port 11303 connected with &lt;IP Addr node1&gt; port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0-10.0 sec&nbsp; 12.5 MBytes&nbsp; 10.0 Mbits/sec
[&nbsp; 3] Sent 401 datagrams</PRE><PRE></PRE></BLOCKQUOTE>
<P><A name=multicast></A>
<B><FONT size=+1>Multicast</FONT></B> 
<P>To test multicast, run several servers with the bind option (-B, --bind) set 
to the multicast group address. Run the client, connecting to the multicast 
group address and setting the TTL (-T, --ttl) as needed. Unlike normal TCP and 
UDP tests, multicast servers may be started after the client. In that case, 
datagrams sent before the server started show up as losses in the first periodic 
report (61 datagrams on arno below). 
<BLOCKQUOTE><PRE><B>node5&gt;</B> iperf -c 224.0.67.67 -u --ttl 5 -t 5
------------------------------------------------------------
Client connecting to 224.0.67.67, UDP port 5001
Sending 1470 byte datagrams
Setting multicast TTL to 5
UDP buffer size: 32.0 KByte (default)
------------------------------------------------------------
[&nbsp; 3] local &lt;IP Addr node5&gt; port 1025 connected with 224.0.67.67 port 5001
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth
[&nbsp; 3]&nbsp; 0.0- 5.0 sec&nbsp;&nbsp; 642 KBytes&nbsp;&nbsp; 1.0 Mbits/sec
[&nbsp; 3] Sent 447 datagrams

<B>node5&gt;</B> iperf -s -u -B 224.0.67.67 -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Binding to local address 224.0.67.67
Joining multicast group&nbsp; 224.0.67.67
Receiving 1470 byte datagrams
UDP buffer size: 32.0 KByte (default)
------------------------------------------------------------
[&nbsp; 3] local 224.0.67.67 port 5001 connected with &lt;IP Addr node5&gt; port 1025
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Jitter&nbsp;&nbsp; Lost/Total Datagrams
[&nbsp; 3]&nbsp; 0.0- 1.0 sec&nbsp;&nbsp; 131 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.007 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 91 (0%)
[&nbsp; 3]&nbsp; 1.0- 2.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.008 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 2.0- 3.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.010 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 3.0- 4.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.013 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 4.0- 5.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.008 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 0.0- 5.0 sec&nbsp;&nbsp; 642 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.008 ms&nbsp;&nbsp;&nbsp; 0/&nbsp; 447 (0%)

<B>node6&gt;</B> iperf -s -u -B 224.0.67.67 -i 1
------------------------------------------------------------
Server listening on UDP port 5001
Binding to local address 224.0.67.67
Joining multicast group&nbsp; 224.0.67.67
Receiving 1470 byte datagrams
UDP buffer size: 60.0 KByte (default)
------------------------------------------------------------
[&nbsp; 3] local 224.0.67.67 port 5001 connected with &lt;IP Addr node5&gt; port 1025
[ ID] Interval&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Transfer&nbsp;&nbsp;&nbsp;&nbsp; Bandwidth&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Jitter&nbsp;&nbsp; Lost/Total Datagrams
[&nbsp; 3]&nbsp; 0.0- 1.0 sec&nbsp;&nbsp; 129 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.778 ms&nbsp;&nbsp; 61/&nbsp; 151 (40%)
[&nbsp; 3]&nbsp; 1.0- 2.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.236 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 2.0- 3.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.264 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 3.0- 4.0 sec&nbsp;&nbsp; 128 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.248 ms&nbsp;&nbsp;&nbsp; 0/&nbsp;&nbsp; 89 (0%)
[&nbsp; 3]&nbsp; 0.0- 4.3 sec&nbsp;&nbsp; 554 KBytes&nbsp;&nbsp; 1.0 Mbits/sec&nbsp; 0.298 ms&nbsp;&nbsp; 61/&nbsp; 447 (14%)</PRE><PRE><HR width="100%"></PRE></BLOCKQUOTE>
<P><A name=ipv6></A>
<DL>
  <DT><B><FONT size=+2>IPv6 Mode</FONT></B> 
  <DD>Download the IPv6 version of this release.<BR>Get the IPv6 address of the node using the 'ifconfig' command.<BR>Use the <FONT color=#000099>-V</FONT> option to indicate that you are using an IPv6 address Please note that we need to explicitly bind the server address also. 
  <P>Server side:<BR><FONT color=#000099> $ iperf -s -V</FONT>
  <P>Client side:<BR><FONT color=#000099>$ iperf -c &lt;Server IPv6 Address&gt; -V </FONT>
  <P>Note: Iperf version 1.6.2 and eariler require a IPv6 address to be explicitly bound
  with the <A HREF="#bind">-B</A> option for the server.</P></DD></DL>
<HR>
<P><A name=repmode></A>
<DL>
  <DT><B><FONT size=+2>Using Representative Streams to measure 
  bandwidth</FONT></B> 
  <DD>Use the -F or -I option. If you want to test how your network performs 
  with compressed / uncompressed streams, just create representative streams and 
  use the -F option to test it. This is usually due to the link layer 
  compressing data. 
  <P>The -F option is for file input.<BR>The -I option is for input from stdin. 
  <P>E.g. <BR>Client: $ <FONT color=#000099> iperf -c &lt;server address&gt; -F &lt;file-name&gt;<BR></FONT>
          <BR>Client: $ <FONT color=#000099> iperf -c &lt;server address&gt; -I </FONT></P></DD></DL>
<P><A name=daemon></A>
<HR>
<DL>
  <DT><B><FONT size=+2>Running the server as a daemon</FONT></B> 
  <DD>Use the -D command line option to run the server as a daemon. Redirect the 
  output to a file.<BR>E.g. <FONT color=#000099>iperf -s -D &gt; 
  iperfLog</FONT>. <FONT color=#000000>This will have the Iperf Server running 
  as a daemon and the server messages will be logged in the file iperfLog. 
</DD></DL>
<HR>
<P><A name=service></A>
<DL>
  <DT><B><FONT size=+2>Using Iperf as a Service under Win32</FONT></B> 
  <DD>There are three options for Win32: 
  <P>
  <DL>
    <DT>-o outputfilename 
    <DD>output the messages into the specified file 
    <DT>-s -D 
    <DD>install Iperf as a service and run it 
    <DT>-s -R 
    <DD>uninstall the Iperf service </DD></DL>
  <P>Examples: 
  <DL>
    <DT><FONT color=#3366ff>iperf -s -D -o iperflog.txt</FONT> 
    <DD>will install the Iperf service and run it. Messages will be reported 
    into "%windir%\system32\iperflog.txt" 
    <P></P>
    <DT><FONT color=#3366ff>iperf -s -R</FONT> 
    <DD>will uninstall the Iperf service if it is installed. 
    <P>Note: If you stop want to restart the Iperf service after having killed 
    it with the Microsoft Management Console or the Windows Task Manager, make 
    sure to use the proper OPTION in the service properties dialog. 
  </P></DD></DL></DD></DL>
<HR>
<!--<P><A name=multicast></A>
<DL>
  <DT><B><FONT size=+2>Running the multicast server and client</FONT></B> 
  <DD>Use the -B option while starting the server to bind it to a multicast 
  address.<BR>E.g. :-<FONT color=#3366ff>iperf -s -u -B 224.0.55.55</FONT>. 

  <P>This will have the Iperf server listening for datagrams (-u) for the 
  address 224.0.55.55(-B 224.0.55.55). 
  <P>Now, start a client sending packets to this multicast address. 
  <P>E.g. : <FONT color=#3366ff>iperf -c 224.0.55.55 -u</FONT>. 
  This will have a UDP client (-u) sending to the multicast address 
  224.0.55.55(-c 224.0.55.55). 
  <P><FONT color=#000000>Start multiple clients or servers as explained above, 
  sending data to the same multicast server. (If you have multiple servers 
  listening on the multicast address, each of the servers will be getting the data) 
</P></DD></DL>
<HR>-->
<!--<A name=adaptive></A>
<DL>
  <DT><B><FONT size=+2>Adaptive window sizes</FONT></B> 
  <DD>Use the -W option on the client to run the client with the adaptive window 
  size. Ensure that the server window size is fairly big for this 
  option.<BR>E.g.. If the server TCP window size is 8KB, it does not help having 
  a client TCP window size of 256KB.<BR>256KB Server TCP Window Size should 
  suffice for most high bandwidth networks. 
  <P>Client changes the TCP window size using a binary exponential 
  algorithm. This means that you may notice that TCP window size suggested may 
  vary according to the traffic in the network, Iperf will suggest the best 
  window size for the current network scenario. 
</DL>
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